"The Legend of Sigurd and Gudrún" is Tolkien’s version – in English narrative verse – of the epic Norse tales of Sigurd the Völsung and the Fall of the Niflungs. Tolkien's son Christopher edited the book and wrote the introduction.

It's not the first time Christopher has published an early work of his father's. In 2007 he edited and brought out "The Children of Húrin," an unfinished fantasy novel.

Little is known about this new work, although a story in today's Guardian suggests that some elements of the story – the slaying of a dragon, the appearance of a gold ring and a broken sword – were later echoed in "The Hobbit" and "The Lord of the Rings."

Tolkienlibrary.com quotes David Brawn, the publishing director of HarperCollins UK, on the book. Brawn says: "[T]he clue as to what the book will contain is in the title.... You will surmise from this that it is not a Middle-earth book, but we are confident that Tolkien fans will be fascinated by it."

"The Children of Húrin" received a mixed reception from the book world.

Jeremy Marshall of The Times said it was (perhaps), "the successor to 'The Lord of the Rings' '" even as Tom Deveson, writing for The Sunday Times, called the book 'barely readable.' "

In the US, however, the book debuted at number one on the New York Times hardcover fiction bestseller list and today there are more than one million copies in print in English worldwide.

HarperCollins, the Guardian suggests, has to hope that the fact that "The Legend of Sigurd and Gudrún" is in narrative verse "won't put off Tolkien's legions of fans."